Deflecting Incoming Asteroids with Paintballs

byNancy AtkinsononOctober 26, 2012

An artist’s rendering of the asteroid Apophis. Credit: ESA

What would be a way to deflect asteroid Apophis if it gets a little too close for comfort in 2029 or 2036? Pew-pew it with 5 tons of white paintballs. Not only would the multiple mini impacts bump the asteroid off course, but the white paint would cover the surface and reflect more sunlight, and over time, the bouncing of photons off its surface could create enough of a force to push the asteroid off its course.
That’s the idea of the winning entry in this year’s Move an Asteroid Technical Paper Competition, sponsored by the United Nations’ Space Generation Advisory Council. Sung Wook Paek, a graduate student in MIT’s Department of Aeronautics and Astronautics, says if timed just right, pellets full of paint powder, launched in two rounds from a spacecraft at relatively close distance, would cover the front and back of an asteroid, more than doubling its reflectivity, or albedo. The initial force from the pellets would bump an asteroid off course; over time, the sun’s photons would deflect the asteroid even more.

Paek said his paintball strategy builds on a solution submitted by last year’s competition winner, who proposed deflecting an asteroid with a cloud of solid pellets. Paek came up with a similar proposal, adding paint to the pellets to take advantage of solar radiation pressure — the force exerted on objects by the sun’s photons.

In his proposal, Paek used the asteroid Apophis as a theoretical test case. This 27-gigaton rock may come close to Earth in 2029, and then again in 2036. Paek determined that five tons of paint would be required to cover the massive asteroid, which has a diameter of 450 meters (1,480 feet). He used the asteroid’s period of rotation to determine the timing of pellets, launching a first round to cover the front of the asteroid, and firing a second round once the asteroid’s backside is exposed. As the pellets hit the asteroid’s surface, they would burst apart, splattering the space rock with a fine, five-micrometer-layer of paint.

But this is not a quick-solution method, as Paek estimates that it would take up to 20 years for the cumulative effect of solar radiation pressure to successfully push the asteroid off its Earthbound trajectory. So if astronomers determine Apophis is a threat in 2029, we’re already too late. Additionally, the paintball method is not an option if estimates change for Asteroid 2012 DA14, which is predicted to pass very close to Earth on February 15, 2013, about 35,000 kilometers (21,000 miles) away.

Plus, using traditional paintballs, or traditional rockets for launching them, may not be ideal. Paek says the violent takeoff may rupture the payload. Instead, he envisions paintballs may be made in space, in ports such as the International Space Station, where a spacecraft could then pick up a couple of rounds of pellets to deliver to the asteroid.

But other substances could also be used instead of paint, such as aerosols that, when fired at an asteroid, “impart air drag on the incoming asteroid to slow it down,” Paek says. “Or you could just paint the asteroid so you can track it more easily with telescopes on Earth. So there are other uses for this method.”

Scientists have said the key to deflecting a dangerous asteroid is to find them early so that a plan can be developed. William Ailor, an asteroid specialist at Aerospace Corporation in California said that the potential for an asteroid collision is a long-term challenge for scientists and engineers.

“These types of analyses are really timely because this is a problem we’ll have basically forever,” Ailor says. “It’s nice that we’re getting young people thinking about it in detail, and I really applaud that.”

Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

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how would the regolith behave to such action? Its not the solid ground we have on Earth. its the powdery form you have in your powderbox. And this layer of loose dirt extends quite a bit more than a finger’s poke.

I seriously doubt that the impact of 5 tons of paint balls is going to have much of influence on a 27 gigaton rock, The paint, however, over a large amount of time may have a significant effect. The trick is to know *what* effect.

“But other substances could also be used instead of paint, such as
aerosols that, when fired at an asteroid, “impart air drag on the
incoming asteroid to slow it down,””

While it might sound silly, it actually isn’t. You put a cloud of gas — any gas — in its way, and as the rock passes through the gas it is affected by friction. That friction slows it down, which changes its orbit. When you slow it down, it drops inward on a new orbit. If done at the right place and time it could make a significant change (relatively speaking) in the overall orbit.

The paintball thing is basically doing the opposite — add outward pressure with both the paint impact and the added reflectivity and the orbit enlarges. With either method you need to thoroughly model the effects of any particular timing, of course, to see whether it actually changes things for the better. 😉

Ok. I guess I misunderstood the aerosol thing. The way it was written I thought they were proposing to coat the rock with an aerosol to slow down the ‘incoming’ asteroid in the Earth’s atmosphere. Even with your more reasonable interpetation I find it difficult to believe we could put enough gas in the way to affect a 27 gigaton rock.

And yes, you would certainly want to model the effects of whatever you do to make *very* sure the effect didn’t cause the rock to hit instead of a close miss.

If your going to go to the effort of sending 5 ton of paint balls up, why not send 5 ton of explosive projectiles? Firethem at the asteroid and set them to detonate after impact. Also, in what way would they be wanting to accelerate it? Slow it down so that it goes into a lower orbit of the sun and perhaps burn up? or accelerate it so that it goes outside earth orbit but can be perhaps used as a mission at a later date as a stepping stone or for materials to build a larger interplanetary craft, but have the risk of it being a threat in the future?

Why white? Wouldn’t black be better? White reflects the photon and little energy is transferred. Like hitting a bowling ball with a ping pong ball where most of the energy remains with the ball as it bounces off. Black absorbs the photons so that the energy is transferred. Like throwing a velcro ball onto a fuzzy target. It stays and transfers its energy.

No. For an effective solar sail, you need the highest reflectivity or albedo as possible. Reflected radiation has a higher radiation pressure against a sail, or an object than an absorbing one. That’s why solar sail designs tend to be mirror-like. Or in this case, as white as possible. Having a black surface would reduce radiation pressure, but helps to heat an object – and emit infra-red light. This still does affect the orbit of an asteroid. Unfortunately I forgot the name of the effect.

I thought the idea of ‘painting’ potential impactors to deflect them has been proposed already some years ago.

Of course it changes the course of the asteroid only marginally and slowly, thus it makes sense only in cases where an impact is well known years ahead. Also, otherwise it might lead to a collision as well as averting it. After avoiding a collision this way, the asteroid will likely need further attention – perhaps we have to re-paint it black decades later…

White causes higher momentum transfer (which is the decisive effect) than black, since momentum of incoming and reflected light are transferred. But the point I guess is the induced change of rflectivity and respective impact on the trajectory. Therefore for a very reflective asteroid black might be better – but most are relatively dark.
Regolith on the asteroid should not be an issue, if the paint is delivered as a fine grained cloud settling gently (relative velocity may have to be low for this, creating a suitable cloud not as easy, as the film suggests).

Explosives instead of paint will likely need more than 5 tons to destroy a dangerous asteroid, and then they create a cloud of debris still hitting earth…

I would rather use some kind of electric gun to spray fine mist of particles at the asteroid. The speed of the particles would likely have to be very slow, so they would settle on the surface and not kick up any dust already there.

For more immediate action I would use explosive projectiles that detonate under the surface and shoot some material out into space.

And of course, in a panic situation there’s the nuclear option. It’s probably rather unpredictable solution, so we would want to have a huge overkill of bombs to break apart and/or deflect any surviving big lumps of rocks before they rain down at us.